An improved synthesis of benzo[b]thiophene and its derivatives using modified montmorillonite clay catalysts

Article abstract of DOI:10.1021/jo00112a010

Methods for the preparation of benzothiophene (3) and its derivatives by cyclization of phenylthioacetals (1) over ZnCl₂-promoted montmorillonite clay are described. Reactions in solution resulted in only moderate (ca. 50%) yields of 3 and the formation of diphenyl disulfide (4) and uncharacterized products. The production of 4 was explained by coordination of 1 via its oxygen atom to active sites of the catalyst and subsequent bimolecular processes. Good to excellent yields (67-98%) of 3 and its derivatives were obtained using vapor phase techniques at 200-300°C to promote the desired intramolecular cyclizations.